Younger Dryas and the Gulf Stream Urban Myth

Every paleo climatology book that discusses the Younger Dryas abrupt cooling event - the Younger Dryas is the name for a period 11,900 years ago when the planet when from interglacial warm to glacial cold with 70% of the cooling occurring in less than a decade and the cold period (during the Younger Dryas 1200 year cold period, the North Atlantic ocean froze each winter to a latitude of Northern Spain and the ice sheets returned to North America, UK, and Northern Europe) lasting for 1200 years, asserts the cause of that abrupt cooling event is somehow related to a melt pulse which interrupts the 'thermalhaline' conveyor and stops the 'Gulf Stream'. How many times have you heard that statement?

There are three urban legends connected with the Younger Dryas, the Gulf Stream, and cyclic abrupt climate change.

1) The majority of heat transfer, the reason why Europe in the winter at latitudes above 60N is warmer than the east coast of the US is due to atmospheric transfer of heat, not due to ocean current transfer of heat. A complete stoppage of the North Atlantic drift current (aka the 'Gulf Stream' which is also an urban legend) would only result in cooling of a few degrees in winter in Europe. Stoppage of the Gulf Stream/North Atlantic Drift current could not and did not cause the Younger Dryas abrupt cooling event. Stoppage of the Gulf stream could not and did not cause the 8200 years before present abrupt cooling event.

What do you mean, the Gulf Stream doesn’t keep Europe warmer than North America? How even scientists are afflicted by urban myths....

There is strong evidence that [phenomenon] and [process] are linked (Obscuro, 1982).

If you persist further, you may find yourself going through the process of looking up a reference, only to be directed to an even earlier one, several more times before you finally reach the canonical document, the one that contains actual data and discussion. And this is what you find:

Based on [invalid data] collected using [method known to be inaccurate] and assuming [long disproven assertion], we conclude [process] causes [phenomenon].

This is how a scientific urban myth is born: by the time you reach a citation 3 times removed from the supporting observations, a conclusion becomes something ‘everyone knows’ despite very few people ever being exposed to the evidence it was based on. “I’m telling you, this paper told that paper that this other paper has compelling evidence for this! Compelling! Well no, I haven’t actually read it myself…”

I don’t believe this is a hugely common phenomenon. But science nowadays is such a vast body of knowledge that there are bound to be a few zombie ideas traipsing around in it, managing to survive because no-one has really properly examined them for a while. It is only when a scientist is inspired to chase one of these ideas back to its origin that they are brought into the light.

Stoppage of the North Atlantic drift current is not 'part of the solution' of cyclic abrupt climate change. The abrupt cooling events in the paleo record are cyclic and have no explanation. The cyclic abrupt cooling events require a massive forcing function to cause the cyclic abrupt cooling.

2) There is no 'thermalhaline conveyor' in the Atlantic to interrupt. Wally Broeker hypothesized the existence of a discrete thermalhaline conveyor with no proof (Wally's paper includes a picture of the hypothesized discrete conveyor which is repeated ad infinitum.) A melt pulse will not stop the North Atlantic drift current as there is no discrete 'thermalhaline current' to interrupt. Data to support this comment will be included in the next comment.

3) Tipping points. It is a fact that there is cyclic abrupt climate change in the paleo record. The Younger Dryas is an example of cyclic abrupt climate change. As the massive forcing mechanism that causes cyclic abrupt climate change is not known Wally Broeker also started the urban legend of 'tipping points'.

The magical tipping point mechanism can only when required amplify a tiny forcing change to cause abrupt change to the earth's climate. If there was massive positive amplification of forcing changes the planet could return to the glacial phase each time there has a major volcanic eruption. If there was positive feedback the planet's temperature would wildly oscillate when there has a major eruption. That is not observed. (More peer reviewed papers and analysis to support the assertion that there is no magical tipping point amplification in later comments.)

Note this is a 2002 published paper. Thirteen years later the Gulf Stream myth continues.

As noted in the 2002 paper, the results of the 2002 paper are not surprising (the results are support by an observed temperature difference of the US west coast winter to US east coast in winter which is due to atmospheric transfer of heat from the ocean rather than ocean currents). The 2002 publish paper notes the results are also supported by results in papers published 40 and 50 years previously.

Is the transport of heat northward by the Gulf Stream and North Atlantic Drift, and its subsequent release into the midlatitude westerlies, the reason why Europe’s winters are so much milder than those of eastern North America and other places at the same latitude? Here, it is shown that the principal cause of this temperature difference is advection by the mean winds. South-westerlies bring warm maritime air into Europe and north westerlies bring frigid continental air into north-eastern North America. Further, analysis of the ocean surface heat budget shows that the majority of the heat released during winter from the ocean to the atmosphere is accounted for by the seasonal release of heat previously absorbed and not by ocean heat-flux convergence. Therefore, the existence of the winter temperature contrast between western Europe and eastern North America does not require a dynamical ocean. ....

...In the current paper we demonstrate that transport of heat by the ocean has little influence on the contrast between the mild winters of western Europe south of 60±N and the harsh ones of eastern North America. North of 60±N the OHT accounts for about a quarter of the contrast by restricting winter sea-ice cover. The dominant cause of the contrast, at both latitudes, is atmospheric advection around the Icelandic Low and the simple maritime–continental climate distinction. The exact positioning and strength of the Icelandic Low is important to the climate contrast and is shown to be greatly influenced by the orographic forcing of the Rocky Mountains. Therefore, the difference in the winter climates arises fundamentally through atmospheric processes and the seasonal storage and release of heat by the ocean mixed layer. This is also all that is required to establish the difference in winter climates between the west coast of Europe and the west coast of North America at the same latitudes.

...Clearly, the atmosphere is doing the lion’s share of the poleward heat transport required to ameliorate climates at mid latitudes. This will be even more so in northern winter when the atmospheric heat transport is greater than its annual mean while the OHT appears to be less than its annual mean (see later)¤.

...The dominance of the atmosphere is far greater than earlier estimates (e.g. Peixoto and Oort 1992) which gave more weight to the ocean. Trenberth and Caron (2001) have compared their results to direct estimates in the ocean and those derived using an inverse method by Ganachaud and Wunsch (2000), and show that the NCEP-derived estimates fall within the error bars of those estimates in the subtropics while the ECMWF-derived estimates are clearly too low. North of 40±N, NCEP and ECMWF estimates agree with each other and with independent direct estimates. Interestingly, these recent estimates are in quantitative agreement with the early estimates of Houghton (1954) and Sverdrup (1957) as presented by Bjerknes (1964).

This is the second part of the urban legend. Wally Broeker drew a picture of a thermalhaline conveyor and included it in a paper. That started the urban legend that there is a discrete thermalhaline conveyor that could be interrupted. Wally later noted his picture was to illustrate a possible hypothesis and said there was no proof that hypothesis was correct. There was no data supplied in Wally's paper to support the assertion of a discrete thermalhaline conveyor.

Ocean probe data indicates there is no discrete thermalhaline conveyor in the Atlantic ocean. The North Atlantic cold dense high latitude water falls and is then distributed locally in the deep ocean. Only 8% follows the path of the hypothesized conveyor route. There is no discrete thermalhaline conveyor in the North Atlantic to be interrupted.

The familiar model of Atlantic ocean currents that shows a discrete "conveyor belt" of deep, cold water flowing southward from the Labrador Sea is probably all wet.

A 50-year-old model of ocean currents had shown this southbound subsurface flow of cold water forming a continuous loop with the familiar northbound flow of warm water on the surface, called the Gulf Stream.

To address those criticisms, Lozier and Bower launched 76 special Range and Fixing of Sound floats into the current south of the Labrador Sea between 2003 and 2006. Those "RAFOS" floats could stay submerged at 700 or 1,500 meters depth and still communicate their data for a range of about 1,000 kilometers using a network of special low frequency and amplitude seismic signals.

But only 8 percent of the RAFOS floats' followed the conveyor belt of the Deep Western Boundary Current, according to the Nature report. About 75 percent of them "escaped" that coast-hugging deep underwater pathway and instead drifted into the open ocean by the time they rounded the southern tail of the Grand Banks.

Eight percent "is a remarkably low number in light of the expectation that the DWBC is the dominant pathway for Labrador Sea Water," the researchers wrote.

Studies led by Lozier and other researchers had previously suggested cold northern waters might follow such "interior pathways" rather than the conveyor belt in route to subtropical regions of the North Atlantic. But "these float tracks offer the first evidence of the dominance of this pathway compared to the DWBC."

"Everybody always thought this deep flow operated like a conveyor belt, but what we are saying is that concept doesn't hold anymore," said Duke oceanographer Susan Lozier. "So it's going to be more difficult to measure these climate change signals in the deep ocean."

3) Tipping points. It is a fact that there is cyclic abrupt climate change in the paleo record. The Younger Dryas is an example of cyclic abrupt climate change. As the massive forcing mechanism that causes cyclic abrupt climate change is not known Wally Broeker also started the urban legend of 'tipping points'.

The magical tipping point mechanism can only when required amplify a tiny forcing change to cause abrupt change to the earth's climate. If there was massive positive amplification of forcing changes the planet could return to the glacial phase each time there has a major volcanic eruption. If there was positive feedback the planet's temperature would wildly oscillate when there has a major eruption. That is not observed. (More peer reviewed papers and analysis to support the assertion that there is no magical tipping point amplification in later comments.)

An abrupt climate change pretty much necessarily implies some sort of tipping point phenomena, even if the exact mechanism isn't known.

Also, the planet's temperature did wildly oscillate for pretty much the entire time period from the spat of exceptionally frequent and powerful volcano eruptions in Europe near the start of the Upper Paleolithic era that are associated with the decline in Neanderthals and the arrival of modern humans in Europe, to the start of the Holocene, ca. 10kya as show by chart below from a PNAS paper (the dark bars at the bottom right are generated by a primitive farming model and are not historical data). The Neolithic revolution was made possible at that point in large part because the climate finally stopped its wild oscillations.

An abrupt climate change pretty much necessarily implies some sort of tipping point phenomena, even if the exact mechanism isn't known.

Also, the planet's temperature did wildly oscillate for pretty much the entire time period from the spat of exceptionally frequent and powerful volcano eruptions in Europe near the start of the Upper Paleolithic era that are associated with the decline in Neanderthals and the arrival of modern humans in Europe, to the start of the Holocene, ca. 10kya as show by chart below from a PNAS paper (the dark bars at the bottom right are generated by a primitive farming model and are not historical data). The Neolithic revolution was made possible at that point in large part because the climate finally stopped its wild oscillations.

While points 1 and 2 may very well be true, the case on point 3 is much weaker.

Hello,
What do you think 'jump' or 'tip' means physically in respect to the planet's climate?

The climate does not 'tip' or 'jump' from one 'state' to another without a physical cause, a physical reason for the observed change. Euphemisms and analogues are used when there is no scientific basis for a claim. There is no magical, 'smart' amplification mechanism that can when required amplify tiny forcing changes to create what is observed. There are no peer reviewed papers that support the assertion of a massive 'smart' amplification mechanism. The 'tip' or 'jump' zombie theory stops people from looking for the physical reason for what is observed. Makes it impossible to solve the problem.

It is a fact that the paleo data shows evidence of cyclic rapid immense climate changes (as the observed changes are cyclic, periodic, a cyclic forcing function is required to explain periodic, cyclic changes to the planet's climate, as opposed to the alternative which is the massive positive feedback hypothesis (which is inferred by the tipping point or jumping state hypothesis) to amplify tiny changes which would create a random oscillating pattern). The last major climate event of this type is called the 8200 year before present event which is a 2C cooling event that lasted for 400 years.

This is the Greenland Ice sheet temperature data for the last 100,000 years. Can you see the cyclic abrupt changes?

You would not accept the assertion that now and then rocks jump up hill. There is no analytical data to support the assertion that planetary climate can or does have massive cyclic changes without a massive forcing function (a massive forcing function that is in proportion to what is observed), a physical reason for what is observed. There is no evidence for a 'smart' amplification mechanism that appears when required to create for example the Younger Dryas abrupt climate change event. The Younger Dryas is an immense climate change (the planet went from interglacial warm to glacial cold during the Younger Dryas with 70% of the cooling occurring in less than a decade. The Younger Dryas lasted for 1200 years. Why so long? Why did the 8200 year before present abrupt cooling event last 400 years?) which is an example of cyclic, abrupt, immense climate change. The Younger Dryas is a type of cyclic abrupt forcing function that is capable of and that does terminate interglacial periods.

The paleo data supports the assertion that there is an unknown cyclic forcing function (the forcing mechanism changes as there are small, medium, and super large changes in the paleo record which all have a periodicity of 1470 years) that causes, is the physical reason, for what is observed. Part of the reason as to why the massive forcing function has not been found, is that multiple zombie theories have filled the void.

The Younger Dryas abrupt climate change event occurred when solar summer insolation at 65N was maximum. That fact and more than a dozen other observations/anomalies/paradoxes indicates that the 'hypothesis' that summer solar insolation at 65N is somehow responsible for, 'part of the solution' for what causes the glacial/interglacial cycle is also a zombie theory.

Solar summer insulation at 65N is currently the same as it was 20,000 years ago during the coldest period of the last 100,000 year glacial period.

This is the Antarctic sheet temperature data for the last 420,000 years. Interglacial periods end abruptly not gradually. A fourth zombie 'theory' which has no connection with the paleo data is that interglacial periods end gradually rather than rapidly. As the graph indicates and multiple peer reviewed papers state based on analysis of data, interglacial periods end abruptly.

Timing of abrupt climate change: A precise clock by Stefan Rahmstorf
Many paleoclimatic data reveal a approx. 1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system; oscillatory modes within the Earth system can be expected to be far more irregular in period.

The time span of the past few million years has been punctuated by many rapid climate transitions, most of them on time scales of centuries to decades or even less. The most detailed information is available for the Younger Dryas-to-Holocene stepwise change around 11,500 years ago, which seems to have occurred over a few decades. The speed of this change is probably representative of similar but less well-studied climate transitions during the last few hundred thousand years. These include sudden cold events (Heinrich events/stadials), warm events (Interstadials) and the beginning and ending of long warm phases, such as the Eemian interglacial. Detailed analysis of terrestrial and marine records of climate change will, however, be necessary before we can say confidently on what timescale these events occurred; they almost certainly did not take longer than a few centuries.

Various mechanisms, involving changes in ocean circulation, changes in atmospheric concentrations of greenhouse gases or haze particles, and changes in snow and ice cover, have been invoked to explain these sudden regional and global transitions. We do not know whether such changes could occur in the near future as a result of human effects on climate. interglacial, with cold and dry phases occurring on a 1500-year cycle, and with climate transitions on a decade-to-century timescale. In the past few centuries, smaller transitions (such as the ending of the Little Ice Age at about 1650 AD) probably occurred over only a few decades at most. All the evidence indicates that most long-term climate change occurs in sudden jumps rather than incremental changes.

According to the marine records, the Eemian interglacial (betazlel: Eemain is the name for the previous interglacial period, we are living at the end of the Holocene interglacial period) ended with a rapid cooling event about 110,000 years ago (e.g., Imbrie et al., 1984; Martinson et al., 1987), which also shows up in ice cores and pollen records from across Eurasia. From a relatively high resolution core in the North Atlantic. Adkins et al. (1997) suggested that the final cooling event took less than 400 years, and it might have been much more rapid.

The event at 8200 BP is the most striking sudden cooling event during the Holocene, giving widespread cool, dry conditions lasting perhaps 200 years before a rapid return to climates warmer and generally moister than the present. This event is clearly detectable in the Greenland ice cores, where the cooling seems to have been about half-way as severe as the Younger Dryas-to-Holocene difference (Alley et al., 1997; Mayewski et al., 1997). No detailed assessment of the speed of change involved seems to have been made within the literature (though it should be possible to make such assessments from the ice core record), but the short duration of these events at least suggests changes that took only a few decades or less to occur.

The Younger Dryas cold event at about 12,900-11,500 years ago seems to have had the general features of a Heinrich Event, and may in fact be regarded as the most recent of these (Severinghaus et al. 1998). The sudden onset and ending of the Younger Dryas has been studied in particular detail in the ice core and sediment records on land and in the sea (e.g., Bjoerck et al., 1996), and it might be representative of other Heinrich events